If you change a single file (particularly in a platform application), then running the application invokes a lot of ant targets and takes a long, long time. Perhaps this could be improved somehow to eliminate any unnecessary steps.

elimination of copy&pasted code in the many existing project types

possibility to do optimizations in one place

write once & use in all project types for certain features (e.g. includes/excludes)

different levels of reuse, something applies to ant projects only, something is more general

possibility for real embedded web browser - could be WebKit which will be included in JDK 6u10 - evaluation was done; because WebKit will not be available via public API in JDK 6u10 using WebKit in NetBeans is postponed

More GUI support for working with window system: defining new modes, editing .wstcref and .settings files

support in build harness for building setup packages (preferably with a bundled JRE), just as you can build ZIP distributions now. see Tonny Kohar's blog for an example, but maybe OpenInstaller is an option too.

create API to allow other people to write their own wizards (maybe with FreeMarker)

make explorer views more matisse friendly - e.g. create their own category in component palette, add setExplorerManager/getExplorerManager to views.